Method of obtaining metallic gallium from combustion gases resulting from any kind of black or brown coal combustion



Sept. 23, 1969 M RYCZEK ETAL 3,468,773

METHOD OF OBTAINING METALLIC GALLIUM FROM COMBUSTION GASES RESULTING FROM ANY KIND 01 BLACK OR BROWN COAL COMBUSTION Filed Aug. 9, 1966 United States Patent METHOD OF OBTAINING METALLIC GALLIUM FROM COMBUSTION GASES RESULTING FROM ANY KIND OF BLACK OR BROWN COAL COMBUSTION Nlichal Ryczek, Ogrodowa 15/61, Krakow 28, Poland; Kornel Wesolowski, Goszczynskiego 24a, Warszawa, Poland; Franciszek Halota, Siersza 131, Poland; Boleslaw Bartoszek, Jordana 35, Katowice, Poland; Tadeusz Marcinow, Lenina 128, Siersza, Poland; Jan Niemiec, Grunwaldzka 299, Trzebinia, Poland; Zygmunt Tyszkowski, Trzehinia 165, Poland; Roman Szczerba, Elektrownia Turow W Turoszowie, Poland; Eugeniusz Kossowski, Mydlana 3, Chrzanow, Poland; Stanislaw Kaleta, Warynskiego 48, Myslachowice, Poland; Eugeniusz Szczerbowski, Grunwaldzka 229; and Mieczyslaw Cholewa, Grunwaldzka 262/4, both of Trzebinia, Poland; and Ryszard Nowak, 22 Stycznia 38, Siersza, Poland Filed Aug. 9, 1966, Ser. No. 571,958 Int. Cl. C22d 1/00 US. Cl. 204105 5 Claims ABSTRACT OF THE DISCLOSURE Obtaining metallic gallium by combustion of mixture of coal containing organic gallium compounds and coal containing inorganic gallium compounds. The mixture also contains organic iron compounds. After combustion the products are processed in steps including electrolysis to obtain metallic gallium deposit.

This invention relates to a method of obtaining metallic gallium from furnace gases resulting from the combustion of coal irrespective of the degree of carbonization, shape or form of occurrence.

According to a known method, metallic gallium is obtained from furnace gases resulting from burning gallium bearing coal of a low degree of carbonization.

Another method is known where metallic gallium or gallium compounds are obtained from dust contained in furnace gases resulting from burning of generator coke gas.

The essential drawback of both these methods is the narrow range of their application.

It is known that gallium compounds yielded by coal having a higher degree of 'carbonization are mostly, and sometimes entirely, inorganic. When burning this grade of coal, no gaseous gallium compounds are educed, or they are educed only in insignificant quantities. In this case, after the coal is burnt, gallium remains entirely in slag or dust such that its concentration is below the value of 0.1%. The obtained products in the form of slag and dust are not of use for direct treatment on an industrial scale according to the known methods.

Long research and experiments resulting in the present invention have proved that it is possible to obtain volatile gallium compounds as a result of burning any kind of coal, including coals containing gallium in the form of inorganic compounds.

According to the method of the present invention, gallium can be separated in the gaseous phase by burning a coal mixture of coal containing organic gallium compounds with humus and coal containing inorganic gallium compounds. The mixture of coal also contains iron in the form of organic compounds. The process of preparing a mixture according to the invention consists in adding to the gallium carrying coal rich in inorganic gallium compounds, such a quantity of coal containing humunous gallium that the proportion of total gallium to the organic gallium should be a minimum of 3:1. Be-

3,468,773 Patented Sept. 23 1969 sides, the mixture of coal must contain organically combined iron in an amount at least 50 times greater by weight than the total gallium content; the natural or artificial moisture content must be above 5% by weight.

The combustion of such a mixture can be performed in any type of boiler furnace in such a way that the combustion gases should contain a minimum of 0.5% of CO and a minimum of 0.001% of H As a result, gallium contained in the coal mixture passes into the gaseous phase in a smaller ratio in the form of hydrides of metallic-organic-methyl type, and in a greater ratio in the form of gallium hydrides and derivatives of iron tetracarbonyl; the total yield of gallium from the burned mixture is more than In the process of burning the coal mixture in accordance with this invention, gallium present in the coal in the form of organic compounds oxidizes giving tetramethyl gallium hydrogen (Reaction 1) which in the presence of CO gives trimethyl gallium by spontaneous decomposition (Reactions II). Gallium present in the coal in the form of inorganic compounds is reduced to give GaH (Reaction III), which reacts with the iron pentacarbonyl formed in the operation to produce [Fe(CO) Ga (Reaction IV).

Thus, all the gallium in the coal takes part in the operation. The organically combined gallium changes almost entirely into trimethyl gallium and gallium hydride, while the inorganically combined gallium forms GaH which reacts with iron pentacarbonyl produced from organic iron to form [Fe(CO) Ga.

Dissociation of trimethyl gallium and [Fe(CO) Ga occurs outside a dust recovering system. Trimethyl gallium reacts partly with S0 and S0 contained in combustion gases forming the hard-to-decompose dimethyl gallium sulphate, Ga(CH .SO [Fe(CO) Ga partly decomposes giving Ga-Fe alloy, Fe Ga. Part of it is not decomposed and escapes. In order to perform a complete decomposition of gallium organic compounds, it is necessary to add some gaseous oxidizing agents like e.g., ozone, or liquids like e.g., nitric acid, or in stable state in the form of cominuted suspended matter e.g., MnO KMnO or Na FeO applying to the cycle simultaneously bulkheads of non-corrosive metal such as e.g., pure Fe or Al, having large surface of contact/net, sponge/. Moreover, capillary silicate in the form of slag cotton, asbestos, etc. may be used. This method gives products including a suspension of metallic gallium.

In the invention it is possible to lower the reaction temperature to about 50 C. which is of further advantage.

Decomposition reaction of gallium volatile compounds takes place according to the present invention:

and the gallium partly reacts further:

2Ga /2 O Ga O The [Fe(CO) also reacts:

2 [Fe (CO) Ga+ 2Fe Ga+2FeO+24CO The above process results in the decomposition of gallium compounds. There is formed soot Fe Ga, Ga, Ga O and GaO.

The gallium concentrate is heated or calcinated at about 400 C., in oxygen atmosphere or in ozonized oxygen or ozone with a small addition of alkali metal carbonate or acid carbonate. The organic compounds are totally decomposed giving CO and water vapor. The soot is burned and the organic compounds decomposed. Gal lium is oxidized or leached to trivalent state reacting with alkali metal carbonates forming the following galliate compounds of alkali according to the following formula:

The content of gallium in concentrate obtained by the method of the invention varies from 1 to 8.5%. Gallium concentrates obtained by known methods contain no more than 0.151.0 of Ga.

After the leaching reaction with alkali metal carbonate or acid carbonate, the gallium concentrate is dissolved in a solution of alkali metal hydroxides in an autoclave in the cold or preferably at about approximately 40 C. and at an increased pressure of above 1.2 atm. The solution obtained contains -20 g./l. of Ga at a ratio of Ga:Al=:1.

The gallium solution is then electrolyzed. Electrolytic gallium is obtained at a current density of 80-120 a./dem. the voltage between the electrodes 'being -17 v. Gallium concentrate thus obtained has 99.0% purity of pure Ga.

Besides gallium contained in the concentrate, a part of the gallium may remain not decomposed in the washing solution. It is obtained by distillation at .a temperature below 100 C. and gallium is separated from the distillate.

After the leaching reaction with alkali metal carbonate or acid carbonate, 0.1-0.3% of the Ga is left undissolved. This undissolved material and the electrolytic deposit are dissolved in sulphuric acid. A solution is obtained with a low gallium concentration of up to 500 mg. of Ga per litre. Into this solution metals having low current densities to cathodic deposition such as copper are introduced. This solution is then electrolyzed at a current density of 0.9-1.5 a./dec. The total amount of gallium is obtained in the cathodic deposit in the form of CuGa alloy containing 12% Ga. The alloy can be further processed by known methods.

Another version of this method is dissolving the deposits in alkaline solution of alkali metal hydroxide. Zinc oxide or hydroxide is added to the solution and the solution is electrolyzed at a current density of 40 to 80 a./dec. The cathodic deposit of metallic zinc and gallium contains 1-8% of Ga. The deposit is then distilled and gallium collected.

Gallium remains in the electrolyte are treated with C0 The regeneration of concentrate is achieved by enriching it as a result of precipitation of gallium remains using CO It is possible to then obtain hydroxides of alkali carbonates using milk of lime and again subjecting the gallium to electrolysis.

The method of this invention is shown in the drawing. Coal mixture containing gallium is collected in container 1 and burnt in the boiler furnace 2. Furnace gases resulting from the burning of this mixture are dedusted in the electrofilter 3 and directed to the reaction towers 4 equipped with aluminum nets 5. Then the furnace gases are washed in a water solution to which an oxidizing agent stored in container 6 is added. The washing solution is poured from tank 7 into a concentrator 8. The concentrated solution is pumped by pump 9 through a centrifuge 27 to reaction towers 4. The initial concentrate is accumulated in tank 19. It is then transferred to mufile furnace 18 with an admixture of sodium carbonate or NaHCO batched from tank 11. Oxygen from electrolyzer 12 is also introduced into this furnace through ozonizer 13. The gallium concentrate is then heated or calcinated at a temperature of about 400 C. and then introduced into an autoclave 14 containing an alkaline solution of alkali metal hydroxide. Oxide sludge from filtration press 16 is introduced into autoclave 14. The obtained solution containing gallium compounds is separated from the insoluble deposit on a vacuum filter 15. The filtrate solution is then introduced into an electrolyzer having a diaphragm where gallium is deposited at the cathode 49.

After the electrolysis, the electrolyte is introduced to column 17, to which CO is supplied from mufile furnace 18.

The gallium oxide deposit obtained is separated by means of the filter press 16, while the solution is regenerated in tank 19 by the introduction of limewater from tank 20 and by separating calcium carbonate sludge 51.

The remaining solution is recirculated to the autoclave 14.

The deposit from filter 15 is fed to the rotary furnace 21 where alkali metal hydroxide from tank 22 is supplied. The calcined product from furnace 21 is fed into the reactor apparatus 23 where it is dissolved in an alkaline water solution-filtrate supplied from vacuum filter 24, after filtering in an atmosphere of air supplied through ducts 23a and separated on a filtration press 25. The gallium-free deposit is drained at point 52 while the solution is fed to electrolyser 26.

The washing solution from centrifuge 27 is introduced into distiller 28. The distillate collects in condenser 29, wherefrom it is supplied to reactor 30 to which also oxidizing agents from tank 31 and an alkaline solution from filter 24 are fed. The gallium containing solution is separated from the deposit containing iron in filtration press 32 and is fed to electrolyzer 26, to which zinc oxide or hydroxide is introduced from tank 33. After electrolysis, the electrolyte is introduced into reactor 34 to which S0 is supplied from muffle furnace 18. The gallium oxide deposit is filtered in filter 35, while the solution is introduced into reactor 36 to which limewater is fed from tank 37. Calcium carbonate deposit is separated on vacuum filter 24, and the obtained solution is introduced into reactors 30 and 23.

Gallium sludge from filter 35 is then supplied to reactor 23. The cathodic Zn-Ga from electrolyser 26 is supplied to the distiller 38 where zinc vapors collect in condenser 39 and are dissolved in reactor 40 in NaOH from tank 41, and are directed through tank 33 to electrolyser 26. The distillation remainder, .an alloy with a considerable gallium content, is further distilled in distiller 42 while zinc chloride vapors are condensed in condenser 43, and gallium trichloride vapors in condenser 44. The gallium condensate is subjected several times to zonal cleaning in induction furnace 45, and then dissolved in water in tank 46, and directed to electrolymer 47. Then the gallium salt is subjected to electrolysis. Metallic gallium is obtained in platinum cathode 50. The electrolyte left after the electrolysis is regenerated in tank 48; from there it is directed to reactor 46 where gallium trichloride is dissolved.

The system shown in the drawing is used as an example illustrating the application of the method claimed in the present invention.

What we claim is:

1. A method of obtaining metallic gallium from furnace gases resulting from the combustion of coal, irrespective of the degree of carbonization, shape and form of occurrence, characterized in that there is prepared a furnace charge comprising a coal mixture in which the gallium content in an organic fraction in relation to the total gallium content in said mixture is a minimum of 1:3, said mixture containing organically combined iron in amount at least 50 times greater by weight than the total gallium content, said mixture also having a moisture content of above 5% by weight, said mixture is then burnt in a boiler furnace system such that the furnace gases contain a minimum of 0.5% CO and a minimum of 0.001% H and gallium compounds are formed which escape together with the furnace gases, the latter, after being dedusted, are reduced down to about 50 C. and oxidizing substances selected from the group consisting of ozone, nitric acid, MnO KMnO and Na FeO are added; the thus obtained gallium material is then heated with a small addition of a material selected from the group consisting of alkali metal carbonate and acid carbonate in an atmosphere selected from the group consisting of oxygen, ozone and ozonized oxygen, at about 400 C.; then the obtained concentrate is leached with an alkali metal carbonate and, after the separation of the insoluble deposit, gallium solution is subjected to electrolysis, at a current density of 80-120 a./sq. decimetre and voltage of 15-17 v., thereby obtaining a gallium concentrate and remaining washing solution; said washing solution is then subjected to distillation at a temperature below 100 C. and the remaining gallium is obtained from the distillate.

2. A method according to claim 1 characterized by that during the leaching and electrolysis milk of lime is added.

3. A method according to claim 1 characterized by that the electrolyte left after the electrolysis and containing gallium residues, is treated with gaseous C0 4. A method according to claim 1 characterized by that undissolved deposit left after leaching is dissolved in sulphuric acid, copper is added to the solution formed and the solution is electrolyzed, thereby forming with the gallium a cathodic copper-gallium alloy deposit containing about 1-2'% of gallium.

5. A method according to claim 1 characterized by dissolving the deposit obtained from leaching in alkaline solution of alkali metal hydroxide, adding a compound selected from the group consisting of zinc oxide and zinc hydroxide to the solution formed, electrolyzing the solution at a current density of -80 a./sq. decimetre, thereby forming an alloy containing l8% of Ga.

References Cited UNITED STATES PATENTS 2,848,398 8/1958 Inagaki 204 JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner 

